Genetic Material in Viruses

Genetic Material in Viruses

• Viruses use genetic material to encode their functions, ensuring continuity and evolution.
• DNA viruses have Deoxyribonucleic Acid (DNA) as their genetic blueprint.
• There are two types of DNA viruses: double-stranded DNA (dsDNA) and single-stranded DNA (ssDNA).

Double-stranded DNA (dsDNA) Viruses

• Possess two complementary DNA strands, wound together in the familiar double helix.
• Examples: Herpesviruses, causing cold sores and genital herpes; Adenoviruses, responsible for a range of illnesses.
• Replicate in the host's nucleus where the cellular DNA is also located.

Single-stranded DNA (ssDNA) Viruses

• Containing just one strand of DNA, these viruses are relatively less common.
• Example: Parvovirus B19, which can cause a mild rash illness called fifth disease.
• Require a host cell to form a complementary strand, which then serves as a template for replication.

RNA Viruses

• Have Ribonucleic Acid (RNA) as their genetic material.
• There are three types of RNA viruses: double-stranded RNA (dsRNA), single-stranded RNA (ssRNA), and satellite RNA.

Double-stranded RNA (dsRNA) Viruses

• Contain complementary RNA strands, but are rarer among RNA viruses.
• Example: Rotavirus, a significant cause of diarrheal disease in infants and young children.
• Replicate primarily in the cytoplasm of the host cell.

Single-stranded RNA (ssRNA) Viruses

• Can be further categorized based on the polarity of RNA.
• There are two types of ssRNA viruses: positive-sense ssRNA (+ssRNA) and negative-sense ssRNA (-ssRNA).

Positive-sense ssRNA (+ssRNA) Viruses

• Their RNA can directly serve as a template for protein synthesis.
• Example: Coronaviruses, including the infamous SARS-CoV-2.

Negative-sense ssRNA (-ssRNA) Viruses

• Their RNA must first be transcribed into a complementary positive-sense RNA by the viral RNA-dependent RNA polymerase enzyme.
• Examples: Influenza virus, which causes seasonal flu; Rabies virus, resulting in a deadly neurological disease.

Structural Diversity

• The structural components of viruses are crucial for protection, host recognition, and entry.
• The capsid, composed of protein subunits known as capsomers, envelopes the virus's genetic material.

Capsid Composition

• There are three types of capsids: helical, icosahedral, and complex.

Helical Capsids

• Resembling rods or threads, these capsids are cylindrical.
• Examples: Tobacco Mosaic Virus, which affects tobacco plants; Rabies virus.
• Function: The helical arrangement provides a protective shield for the nucleic acid.

Icosahedral Capsids

• Resembling 20-sided dice, these capsids are nearly spherical but polygonal.
• Examples: Polioviruses; Adenoviruses.
• Function: This compact shape offers a stable environment for the viral genetic material.

Complex Capsids

• These capsids exhibit both helical and icosahedral properties or might have additional components.
• Example: Bacteriophages.
• Function: Tail fibres in bacteriophages, for instance, aid in attaching to specific bacterial cells.

Viral Envelopes

• The presence or absence of an outer envelope further distinguishes viruses.

Enveloped Viruses

• Possess an outer lipid bilayer membrane, typically derived from the host cell's own membrane during viral replication or budding.
• Function: The envelope may contain viral proteins or glycoproteins essential for binding to host cells, facilitating viral entry.
• Examples: HIV, Influenza viruses.
• Vulnerability: They are more susceptible to environmental factors and detergents.

Non-enveloped Viruses

• Lacking the lipid bilayer, they're more robust structurally.
• Function: They rely on their capsid alone for protection and interaction with host cells.
• Examples: Norovirus, responsible for stomach flu; Rhinovirus, causing common cold.